Canadian scientists have identified the factors that cause distress after sleep paralysis, a psychological phenomenon of which little was previously known, according to a study.

Sleep paralysis is a distressing phenomenon often accompanied by vivid sensory or perceptual experiences, which can include complex and disturbing hallucinations and intense fear, which is often experienced by people immediately before sleeping or waking up.

For some people, sleep paralysis is a once-in-a-lifetime experience; for others, it can be a frequent, even nightly, phenomenon, Science Daily reported.

The study, conducted by researchers James Allan Cheyne and Gordon Pennycook of the University of Waterloo in Canada, was published published in Clinical Psychological Science, a journal of the Association for Psychological Science, and explores the factors associated with distress after sleep paralysis episodes.